Before Big Bang: Light Shed on "Previous Universe"

Mason Inman for National Geographic News

July 3, 2007

We may be able to get a glimpse of what happened before the big bang, thanks to a new study—but only a glimpse. The big bang has traditionally been seen as the beginning of everything—space, time, matter, and energy. But researchers are developing sophisticated new theories to look ever further back in time, to what happened just fractions of a second after big bang itself. In the new research, Martin Bojowald of Pennsylvania State University pushes one of these theories back even further—to the time of a purported previous universe that contracted and "bounced" to form our own. The new study comes with some bad news, though. It suggests that the universe suffers from "cosmic forgetfulness," so that we can never be able to find out too much about what came before our big bang. The new study appeared online this week in the journal Nature Physics. Theory of Everything Our universe is expanding outward in every direction, implying that it originally exploded out from a single point about 14 billion years ago. The further we look back in time, the smaller and hotter the universe gets. At the beginning of time, most traditional theories speculate, the universe was infinitely hot and had no size at all. But no one knows for sure, since textbook physics suffers a meltdown and gives nonsensical answers when used to describe what the universe was like at moment of the big bang, Bojowald says. These theories "tell us energies were infinitely large," Bojowald said. "It doesn't have any meaning for us." This is one reason why researchers have been toiling for decades to unite two main branches of physics—gravity and quantum mechanics. Gravity rules on cosmic scales, while quantum mechanics dictates the behavior of tiny particles like electrons and quarks. While each theory has been wildly successful, they remain contradictory. Uniting these two branches of physics would peel back time further and allow scientists to figure out exactly what the big bang was. But creating such a "theory of everything" has been a longstanding and difficult goal that has stumped every physicist who has attempted it, including Albert Einstein. Big Bounce, Not Big Bang Bojowald used a leading approach to this quandary known as loop quantum gravity, a competitor to the more popular approach known as string theory. Both theories are still incomplete and unproven, and each suggests very strange ideas about the fundamental nature of the universe. In loop quantum gravity, for instance, space and time are not smooth and continuous but rather divided up into tiny chunks. In this mathematical approach, everything is jerky and blocky—although on such a tiny scale that it doesn't affect daily life. Nothing can occupy a space smaller than the smallest chunk of space, and nothing can happen any faster than this shortest moment of time. This implies that the universe could never shrink down beyond a certain size. So when it was at its most compact, where did that tiny ball of energy and matter come from? It could have come from the universe before our own, Bojowald argues. Unlike our expanding universe, this earlier universe was contracting back toward a point, he says. When it reached its most compact, it hit the barrier dictated by loop quantum gravity. Then it "bounced back" outward, forming a new, expanding universe. Certain Uncertainty So if our universe came from an earlier universe, it's natural to wonder what that ancestral universe was like. But there's a problem: Quantum physics must have played a key role in the hot, dense state around the time of the "big bounce." Things behave very oddly in the quantum world. An object that appears to be in one spot when you first glimpse it can be in another spot when you look again. This jumpiness, known as uncertainty, is built into quantum physics. Building better measuring devices won't get around it. If the whole universe suffered from these jitters, "it could be impossible to have life," Bojowald said. In our universe, however, such weirdness only happens on very, very tiny scales. But what about the universe that came before us? When the universe goes through a big bounce, Bojowald showed, the amount of uncertainty before and after the bounce have little relation to each other. So there's a veil that screens out much of what we would want to know about the earlier universe. This also implies that a universe is never the same before and after a bounce. "The eternal recurrence of absolutely identical universes would seem to be prevented by the ... cosmic forgetfulness," Bojowald said. (Related: "Universe Reborn Endlessly in New Model of the Cosmos" [April 25, 2002].) Even that kind of cycle might be coming to an end, since scientists now believe that the universe is expanding faster every day, not slowing down as would be expected. So a re-contraction seems extremely unlikely under our current understanding. Question of Accuracy Whether Bojowald's model is believable or not, however, depends on whether the version of loop quantum gravity that he used is accurate. Thomas Thiemann, of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, called Bojowald's approach a "drastic simplification." But it may turn out to be fairly accurate anyway, Thiemann said. If so, then it is "the cleanest derivation of a pre-big bang scenario that any physical theory has delivered so far," he added. It's "much cleaner than in string-theory-inspired models."

Time Before Time
By Phil Berardelli
ScienceNOW Daily News
5 July 2007

A cosmologist has created a mathematical model that he says shows space-time, contrary to common wisdom, did not begin with the Big Bang. Instead, the model suggests a universe pretty much like the one we live in today existed before the event, except it was contracting instead of expanding. If ever proven, the idea could force a complete rethinking of the origins of the cosmos and perhaps even open a doorway to an endless future.
The Big Bang--the sudden and extremely rapid expansion of space-time that began 13.7 billion years ago--is generally accepted among scientists as the beginning of the universe. However, they have long puzzled over a paradox that the event caused in the mathematical calculations of Einstein's Theory of General Relativity. At the moment of the Big Bang, everything was thought to be crammed into a singularity--a space with no dimensions--that also contained infinite density. Einstein couldn't explain how such a state could give rise to a universe of finite density and possibly finite dimensions. Theoretical physicist Sean Carroll of the California Institute of Technology in Pasadena put it more succinctly: "Everyone's calculations show the universe started from a singularity," he says, "but no one believes it."

Most cosmologists have come to think that quantum mechanics--something unknown during Einstein's time--could hold the key to this conundrum. According to quantum mechanics, random activity on an extremely tiny scale can affect the outcome of events vast distances away and involving gigantic masses. For example, adherents of this theory believe that the current universe turned out so lumpy--with clusters of galaxies in some areas and nearly empty space in others--because of quantum fluctuations at the moment of the Big Bang.

But so far quantum mechanics has not been able to explain where the universe came from in the first place. Although most cosmologists think it sprang forth from nothingness along with the forces of nature, theoretical physicist Martin Bojowald of Pennsylvania State University in University Park thinks his mathematical model points to something even stranger: The cosmos is a leftover from a previous manifestation of existence.

Bojowald's model is based on a new and developing line of theoretical reasoning called Loop Quantum Gravity, which attempts to reconcile Einstein's theory with quantum mechanics. As Bojowald reported online in the 1 July Nature Physics, the model shows that at the moment of the Big Bang, the current universe had a minimum volume that was not zero and carried a huge but finite amount of energy. Furthermore, the calculations strongly suggest that the current universe actually received a kick–start from the dying epoch of a previous, contracting universe. They do so by showing that the previous universe could not have compacted itself into a singularity, as general relativity predicts, because at extremes of temperature and pressure, gravity becomes repulsive instead of attractive. As a result, gravitational energy grew so large as the previous universe contracted that it created a "Big Bounce," as Bojowald calls it, which ignited the current expansion. With some luck, he says, it might be possible to find clues about what the previous universe was like from more detailed observations and models of quantum mechanics.

Far-fetched or not, Carroll thinks Bojowald's model represents a "good thing to be doing," because somehow cosmologists are going to have to resolve the singularity dilemma, and although his conclusions might not provide the correct answer, it's "not premature to be asking the questions."